This invention relates to the art of plane grinding with the aid of a bell grinding-wheel working axially, and more particularly to a machine for grinding at least one flat surface with the aid of at least one rotary grinding-wheel, of the type having a frame supporting at least one rotary grinding-wheel, means for driving the grinding-wheel rotatingly, positioning means suitable for receiving and placing parts having a surface to be ground, mutual translatory displacement means for displacement between the rotary grinding-wheel and the parts disposed in the positioning means, and a diamond cutter-wheel for dressing or redressing the grinding-wheel.
The invention further relates to a method of grinding at least one flat surface with the aid of at least one rotary grinding-wheel.
The various principles of this art, as well as the principles of grinding in general, are best defined at the present time in the manual entitled Begriffe der Schleiftechnik, by E. Salgie and H. Brandin, published by Vulkan Verlag in Essen, West Germany.
In the prior art, the grinding of flat surfaces with the aid of a bell grinding-wheel working axially has been practiced in a manner which leaves "jagged" inequalities within the prescribed zone of tolerance. Chiefly known are ordinary grinding-wheels necessitating frequent redressing (also called truing or diamond grinding), for the grinding-wheel, while working, not only wears down but tends to gum up. Generally, but not necessarily, the grinding-wheel is trued at the same time as it is reset to the minimum dimension of the tolerance. In normal operation, the grinding-wheel does not sink axially, so that the thickness of the ground workpiece increases within the zone of tolerance. When the maximum dimension permitted by the tolerance is reached, or almost reached, this is detected by a comparator acting upon the ground workpieces, and the grinding-wheel is disengaged from the grinding zone to be lowered, then trued or dressed, operation then resuming from the minimum dimension of the tolerance.
Also known are so-called "self-dressing" grinding-wheels. These have the distinctive characteristic of always remaining very abrasive inasmuch as blunted particles are automatically torn away owing to the special composition of the bonding agent of the grinding-wheel. However, the amount of wear can never be foreseen, and the thickness of the workpiece must likewise be measured with the aid of a comparator. Wear naturally takes place more rapidly than with a grinding-wheel of the normal type, and the maximum dimension of the tolerance is reached rather quickly. When this situation is detected, the grinding-wheel is lowered slightly during the next few grinding operations, by at least more than the extent of the attrition. The dimension then begins to decrease within in the tolerance, and lowering of the grinding-wheel is stopped when the minimum dimension is reached. Thus, within the prescribed tolerances, there is likewise a "jagged" distribution of the real dimensions.
The second type of known grinding-wheel mentioned above has the drawback of being expensive, all the more so as attrition is more rapid. It also has quite some drawbacks from the point of view of the environment; and although it eliminates the necessity for truing, it does not eliminate the drawback of "jagged" distribution of dimensions.
Neither do French Pat. No. 2,106,167 and Swiss Pat. No. 362,618 offer any solution to the drawbacks set forth. Thus, the French patent describes a machine of the type to which the present invention relates but does not propose permanent and continuous dressing of the grinding-wheel; no dressing cutter is provided for that purpose. The Swiss patent, on the other hand, does provide for such cutter-wheels, but continuous dressing is not ensured there, either, for these cutters operate alternately, and dressing takes place conventionally, whenever it proves to be necessary by interrupting the grinding operations.